Re: [PATCH] drm/amdgpu: Count disabled CRTCs in commit tail earlier

From: Andrey Grodzovsky
Date: Fri Jun 22 2018 - 21:04:19 EST

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In reply to: Lyude Paul: "Re: [PATCH] drm/amdgpu: Count disabled CRTCs in commit tail earlier"
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On 06/22/2018 02:56 PM, Lyude Paul wrote:

On Fri, 2018-06-22 at 13:34 -0400, Andrey Grodzovsky wrote:

On 06/21/2018 04:48 PM, Lyude Paul wrote:

This fixes a regression I accidentally reduced that was picked up by
kasan, where we were checking the CRTC atomic states after DRM's helpers
had already freed them. Example:

==================================================================
BUG: KASAN: use-after-free in
amdgpu_dm_atomic_commit_tail.cold.50+0x13d/0x15a [amdgpu]
Read of size 1 at addr ffff8803a697b071 by task kworker/u16:0/7

CPU: 7 PID: 7 Comm: kworker/u16:0 Tainted: G O 4.18.0-
rc1Lyude-Upstream+ #1
Hardware name: HP HP ZBook 15 G4/8275, BIOS P70 Ver. 01.21 05/02/2018
Workqueue: events_unbound commit_work [drm_kms_helper]
Call Trace:
dump_stack+0xc1/0x169
? dump_stack_print_info.cold.1+0x42/0x42
? kmsg_dump_rewind_nolock+0xd9/0xd9
? printk+0x9f/0xc5
? amdgpu_dm_atomic_commit_tail.cold.50+0x13d/0x15a [amdgpu]
print_address_description+0x6c/0x23c
? amdgpu_dm_atomic_commit_tail.cold.50+0x13d/0x15a [amdgpu]
kasan_report.cold.6+0x241/0x2fd
amdgpu_dm_atomic_commit_tail.cold.50+0x13d/0x15a [amdgpu]
? commit_planes_to_stream.constprop.45+0x13b0/0x13b0 [amdgpu]
? cpu_load_update_active+0x290/0x290
? finish_task_switch+0x2bd/0x840
? __switch_to_asm+0x34/0x70
? read_word_at_a_time+0xe/0x20
? strscpy+0x14b/0x460
? drm_atomic_helper_wait_for_dependencies+0x47d/0x7e0 [drm_kms_helper]
commit_tail+0x96/0xe0 [drm_kms_helper]
process_one_work+0x88a/0x1360
? create_worker+0x540/0x540
? __sched_text_start+0x8/0x8
? move_queued_task+0x760/0x760
? call_rcu_sched+0x20/0x20
? vsnprintf+0xcda/0x1350
? wait_woken+0x1c0/0x1c0
? mutex_unlock+0x1d/0x40
? init_timer_key+0x190/0x230
? schedule+0xea/0x390
? __schedule+0x1ea0/0x1ea0
? need_to_create_worker+0xe4/0x210
? init_worker_pool+0x700/0x700
? try_to_del_timer_sync+0xbf/0x110
? del_timer+0x120/0x120
? __mutex_lock_slowpath+0x10/0x10
worker_thread+0x196/0x11f0
? flush_rcu_work+0x50/0x50
? __switch_to_asm+0x34/0x70
? __switch_to_asm+0x34/0x70
? __switch_to_asm+0x40/0x70
? __switch_to_asm+0x34/0x70
? __switch_to_asm+0x40/0x70
? __switch_to_asm+0x34/0x70
? __switch_to_asm+0x40/0x70
? __schedule+0x7d6/0x1ea0
? migrate_swap_stop+0x850/0x880
? __sched_text_start+0x8/0x8
? save_stack+0x8c/0xb0
? kasan_kmalloc+0xbf/0xe0
? kmem_cache_alloc_trace+0xe4/0x190
? kthread+0x98/0x390
? ret_from_fork+0x35/0x40
? ret_from_fork+0x35/0x40
? deactivate_slab.isra.67+0x3c4/0x5c0
? kthread+0x98/0x390
? kthread+0x98/0x390
? set_track+0x76/0x120
? schedule+0xea/0x390
? __schedule+0x1ea0/0x1ea0
? wait_woken+0x1c0/0x1c0
? kasan_unpoison_shadow+0x30/0x40
? parse_args.cold.15+0x17a/0x17a
? flush_rcu_work+0x50/0x50
kthread+0x2d4/0x390
? kthread_create_worker_on_cpu+0xc0/0xc0
ret_from_fork+0x35/0x40

Allocated by task 1124:
kasan_kmalloc+0xbf/0xe0
kmem_cache_alloc_trace+0xe4/0x190
dm_crtc_duplicate_state+0x78/0x130 [amdgpu]
drm_atomic_get_crtc_state+0x147/0x410 [drm]
page_flip_common+0x57/0x230 [drm_kms_helper]
drm_atomic_helper_page_flip+0xa6/0x110 [drm_kms_helper]
drm_mode_page_flip_ioctl+0xc4b/0x10a0 [drm]
drm_ioctl_kernel+0x1d4/0x260 [drm]
drm_ioctl+0x433/0x920 [drm]
amdgpu_drm_ioctl+0x11d/0x290 [amdgpu]
do_vfs_ioctl+0x1a1/0x13d0
ksys_ioctl+0x60/0x90
__x64_sys_ioctl+0x6f/0xb0
do_syscall_64+0x147/0x440
entry_SYSCALL_64_after_hwframe+0x44/0xa9

Freed by task 1124:
__kasan_slab_free+0x12e/0x180
kfree+0x92/0x1a0
drm_atomic_state_default_clear+0x315/0xc40 [drm]
__drm_atomic_state_free+0x35/0xd0 [drm]
drm_atomic_helper_update_plane+0xac/0x350 [drm_kms_helper]
__setplane_internal+0x2d6/0x840 [drm]
drm_mode_cursor_universal+0x41e/0xbe0 [drm]
drm_mode_cursor_common+0x49f/0x880 [drm]
drm_mode_cursor_ioctl+0xd8/0x130 [drm]
drm_ioctl_kernel+0x1d4/0x260 [drm]
drm_ioctl+0x433/0x920 [drm]
amdgpu_drm_ioctl+0x11d/0x290 [amdgpu]
do_vfs_ioctl+0x1a1/0x13d0
ksys_ioctl+0x60/0x90
__x64_sys_ioctl+0x6f/0xb0
do_syscall_64+0x147/0x440
entry_SYSCALL_64_after_hwframe+0x44/0xa9

The buggy address belongs to the object at ffff8803a697b068
which belongs to the cache kmalloc-1024 of size 1024
The buggy address is located 9 bytes inside of
1024-byte region [ffff8803a697b068, ffff8803a697b468)
The buggy address belongs to the page:
page:ffffea000e9a5e00 count:1 mapcount:0 mapping:ffff88041e00efc0 index:0x0
compound_mapcount: 0
flags: 0x8000000000008100(slab|head)
raw: 8000000000008100 ffffea000ecbc208 ffff88041e000c70 ffff88041e00efc0
raw: 0000000000000000 0000000000170017 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff8803a697af00: fb fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff8803a697af80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc

ffff8803a697b000: fc fc fc fc fc fc fc fc fc fc fc fc fc fb fb fb

^
ffff8803a697b080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff8803a697b100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================

So, we fix this by counting the number of CRTCs this atomic commit disabled
early on in the function before their atomic states have been freed, then
use
that count later to do the appropriate number of RPM puts at the end of the
function.

I am a bit not clear, are you saying that the problem was the 'in the
middle' commit (cursor ioctl) doing

drm_atomic_state_default_clear->dm_crtc_destroy_state->kfree(state)

where the state is the one you access from from the non blocking part of
page flip though old_crtc_state->active?

The problem is that (see the comment in drivers/gpu/drm/drm_atomic_helper.c:2065
) it's unsafe to touch any of the old_crtc_state structures after
drm_atomic_helper_commit_hw_done() is called, as it's likely that they've been
freed already.

IÂ am not sure about that, the comment in drm_atomic_helper_commit_hw_done says that
"the driver is not allowed to read or change any permanent software
or hardware modeset state" I interpret it as not the old_crtc_state but as the new_crtc_state or crtc->state after
drm_atomic_helper_swap_state completed.Â It means that if you touch crtc->state after drm_atomic_helper_commit_hw_done
you actually could already be accessing a state which belong to the next atomic commit after you.
It really looks like cursor's atomic commit sneaks in in a middle of page flip between the page flip IOCTL
and it's commit_tail part and swaps away crct->state to his own new state and release the 'old' state which is not really
old yet and needs to be used by the tail part of page flip. This makes sense since do_aquire_global_lock we use in amdgpu_dm_atomic_check
to serialize against concurrent atomic_commitsÂ is not called for case of cursor plane and so it may race against any commit_tail in flight...
Not sure why we haven't seen this problem before.
Obviously your fix makes the problem go away since you stopped accessing the new_crtc_state and not the old_crtc_state but the root problem
seems to me still there.

Andrey

Andrey

Fixes: 97028037a38ae ("drm/amdgpu: Grab/put runtime PM references in
atomic_commit_tail()")
Signed-off-by: Lyude Paul <lyude@xxxxxxxxxx>
Cc: Michel DÃnzer <michel@xxxxxxxxxxx>
Reported-by: Michel DÃnzer <michel@xxxxxxxxxxx>
---
drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 10 ++++++----
1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
index f9add85157e7..689dbdf44bbf 100644
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
@@ -4206,6 +4206,7 @@ static void amdgpu_dm_atomic_commit_tail(struct
drm_atomic_state *state)
struct drm_connector *connector;
struct drm_connector_state *old_con_state, *new_con_state;
struct dm_crtc_state *dm_old_crtc_state, *dm_new_crtc_state;
+ int crtc_disable_count = 0;
drm_atomic_helper_update_legacy_modeset_state(dev, state);
@@ -4410,6 +4411,9 @@ static void amdgpu_dm_atomic_commit_tail(struct
drm_atomic_state *state)
struct amdgpu_crtc *acrtc = to_amdgpu_crtc(crtc);
bool modeset_needed;
+ if (old_crtc_state->active && !new_crtc_state->active)
+ crtc_disable_count++;
+
dm_new_crtc_state = to_dm_crtc_state(new_crtc_state);
dm_old_crtc_state = to_dm_crtc_state(old_crtc_state);
modeset_needed = modeset_required(
@@ -4463,11 +4467,9 @@ static void amdgpu_dm_atomic_commit_tail(struct
drm_atomic_state *state)
* so we can put the GPU into runtime suspend if we're not driving
any
* displays anymore
*/
+ for (i = 0; i < crtc_disable_count; i++)
+ pm_runtime_put_autosuspend(dev->dev);
pm_runtime_mark_last_busy(dev->dev);
- for_each_oldnew_crtc_in_state(state, crtc, old_crtc_state,
new_crtc_state, i) {
- if (old_crtc_state->active && !new_crtc_state->active)
- pm_runtime_put_autosuspend(dev->dev);
- }
}

Next message: Andrea Parri: "Re: [PATCH] MAINTAINERS: Add Daniel Lustig as a LKMM reviewer"
Previous message: Yang Shi: "Re: [RFC v2 PATCH 2/2] mm: mmap: zap pages with read mmap_sem for large mapping"
In reply to: Lyude Paul: "Re: [PATCH] drm/amdgpu: Count disabled CRTCs in commit tail earlier"
Next in thread: Andrey Grodzovsky: "Re: [PATCH] drm/amdgpu: Count disabled CRTCs in commit tail earlier"
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